Hydrophilic, elastomeric, pressure-sensitive adhesive

ABSTRACT

The present invention concerns a novel water-insoluble, hydrophilic, pressure-sensitive adhesive that has a number of unique characteristics including being elastomeric and ultraconformable. This adhesive includes an irradiation cross-linked synthetic organic polymer having a three-dimensional matrix, and an adhesive plasticizer. The plasticizer includes a substantially non-volatile elasticizer. The adhesive is useful either as a coating on a supporting web-like substrate or as a self-supporting layer. Also provided are various articles made using the adhesive such as a bandage or ostomy device, a method of making the adhesive, and methods of using the adhesive. 
     In one embodiment, the adhesive is electroconductive, and is useful for attaching an electrically conductive member of an electrode to a selected surface such as mammalian tissue. Also provided is an electrode having a layer of this adhesive, and a method of adhering this electrode to mammalian tissue.

This is a continuation of application Ser. No. 528,679, filed on Sept.1, 1983, now abandoned, which is a continuation-in-part of applicationSer. No. 352,268, filed Feb. 25, 1982, now abandoned.

TECHNICAL FIELD

This invention relates to a novel pressure-sensitive adhesive, andparticularly relates to a water-insoluble, hydrophilic, elastomeric,pressure-sensitive adhesive. This invention additionally relates to asupportive web-like substrate such as that of an ostomy appliance,coated with this adhesive, to a self-supporting layer of the adhesive,to various articles made of this self-supporting layer, to methods ofusing the self-supporting layer, to a method of making the adhesive, toa type of the adhesive that is electroconductive, and to an electrodesuch as an electrosurgical return electrode comprising this type of theadhesive.

BACKGROUND ART

A polymeric hydrophobic substance is the most common type ofconventional pressure-sensitive adhesive used to secure substrates tothe human body. The majority of all adhesive bandages are made with thisbroad class of adhesive, which is used as a thin film. These polymerichydrophobic substances are frequently produced by homopolymerization orcopolymerization of one or more vinyl type monomers, especially acrylicesters, methacrylic esters, vinyl alcohol esters and vinyl ethers.Natural rubber and gum have also found use in conventional adhesiveformulae.

When these prior art thin film, hydrophobic, polymeric,pressure-sensitive adhesives are used to secure a device such as an EKGmonitoring electrode or to secure a bandage, removal frequently causestrauma, discomfort and soreness to the skin to which the adhesive wasadhered. Skin trauma of this type may take the form of pulled hair,bruises, erythema, edema, blistering, removal of some epidermis, ortearing of the skin. The severity of the discomfort and trauma appearsto be greater when the adhesive is allowed to contact the skin for anextended time. Frequently, EKG monitoring electrodes and postsurgicalbandages are left on a patient's skin for up to a week and sometimeslonger. Thus, the removal of these bandages and electrodes, quite often,is very painful, and soreness persists for some time.

Hydrophilic polymeric pressure-sensitive adhesives are also known in theprior art. Adhesives of this type are much less common than hydrophoboicpressure-sensitive adhesives. Major uses of hydrophilicpressure-sensitive adhesives include use as an ostomy adhesive and as aconductive adhesive for securing an electrode to the human body. Thesepressure-sensitive adhesives are much less likely to cause skin traumathan the hydrophobic-type adhesives.

Some hydrophilic-type adhesives are made by chemically cross-linking apolymeric material to form the adhesive. Illustrative of this type ofprior art are U.S. Pat. No. 3,998,215 to Anderson et al, U.S. Pat. No.4,125,110 to Hymes, British Patent Application No. 2,034,184 of Hymes,U.S. Pat. No. 4,066,078 to Berg, and U.S. Pat. No. 4,094,822 to Kater.The adhesive of each of these documents is used in a patient electrode,and is conductive per se or provided with conductivity by, for example,using the adhesive to bond strands of a conductive material. In theAnderson et al, Hymes and Kater documents, it is stated that theadhesive is formed from an aqueous solution of the polymeric material.

In the Anderson et al patent, a porous webbed material is dipped into anaqueous solution of a hydrogel former, for example, polyvinyl alcohol,to wet the webbed material, excess solution is scraped off, and thewebbed material is then dipped into a solution of a gel-forming agent ora cross-linker for the hydrogel former, in order to form a hydrogelthroughout the webbed material. The hydrogel is said to be lightlyadherent to the body surface but sufficiently cohesive so that noresidue remains upon removal thereof.

The Hymes patent relates to an electrode having an electricallyconductive adhesive that contains a hydrophilic polysaccharide material(karaya), a hydric alcohol (glycerin) to provide plasticity, anelectrolytic salt and propylene glycol. An alternate embodiment of thisadhesive includes additive materials for cross-linking the hydrophilicpolysaccharide material. These chemical cross-linking agents are said toinclude, for example, gelatin, polyvinyl acetate, certain polyesters andcalcium salts.

The British patent application in the name of Hymes is similar to theU.S. patent to Hymes. The adhesive of this document is formed from drykaraya gum powder and a non-volatile liquid carrying either an ionizablesalt or finely powdered silver or aluminum. In an alternate embodiment,the adhesive is comprised of 15-70% aqueous polyacrylic acid (25%concentration), 15-45% karaya, 10-35% water, 0-35% isopropyl alcohol,and 1-3% electrolyte. Additive materials for chemically cross-linkingthe karaya are said to include polymers such as vinyl acetate-ethylenecopolymers and polyacrylic acid. At page 7, lines 48-50, it is mentionedthat the substrate compound can be subjected to radiation to inhibitmicrobial growth, and that such radiation should be below 2.5 megaradsgamma radiation.

The Kater patent pertains to an electrode having an adhesive-electrolytematerial. Polyvinyl alcohol adhesives are said to be preferred, and aformulation is provided for an adhesive of this type, in which there ispresent 15-25% polyvinyl alcohol having a degree of polymerization equalto 1700 and being 88% hydrolyzed, and 5-10% glycerol. Suitably, theadhesive-electrolyte material is based upon polyvinylpyrrolidone (PVP),polyacrylamide or polyvinylpyridines.

The Berg patent, mentioned above, is concerned with an electrode havingan electrically conductive, hydrophilic adhesive that is a chemicallycross-linked hydrophilic interpolymer composition. The startingmaterials for preparing this interpolymer composition may be (a) anester of an α,β-olefinically unsaturated carboxylic acid and amonohydric or polyhydric alcohol having a terminal quaternary ammoniumgroup, and (b) an α,β-olefinically unsaturated comonomer.

Other documents relating to an adhesive for use in a patient electrodeinclude British Patent Application No. 2,045,088 in the name ofLarimore, U.S. Pat. No. 4,237,886 to Sakurada et al, U.S. Pat. No.4,243,051 to Wittemann, U.S. Pat. No. 4,243,052 to Bailey, U.S. Pat. No.4,248,247 to Ware et al, U.S. Pat. No. 4,267,840 to Lazar et al, U.S.Pat. No. 3,547,105 to Paine, U.S. Pat. No. 3,565,059 to Hauser et al,U.S. Pat. No. 3,607,788 to Adolph et al, U.S. Pat. No. 3,911,906 toReinhold, Jr., U.S. Pat. No. 3,993,049 to Kater, U.S. Pat. No. 4,008,721to Burton, U.S. Pat. No. 4,016,869 to Reichenberger, U.S. Pat. No.4,067,342 to Burton, U.S. Pat. No. 4,112,941 to Larimore, U.S. Pat. No.4,141,366 to Cross, Jr. et al, U.S. Pat. No. Re. 24,906 to Ulrich, U.S.Pat. No. 3,845,757 to Weyer and U.S. Pat. No. 3,265,638 to Goodman etal. The Larimore British Patent application and the Sakurada et al,Wittemann, Bailey, Ware et al and Lazar et al patents appear to beconcerned with adhesives based upon cross-linked polymers. The patentsto Reinhold, Jr., Larimore, Burton and Cross, Jr. et al pertain to anadhesive material based upon an acrylic polymer. Of these patents, thepatent to Reinhold, Jr., has electrically conductive particles dispersedthroughout the adhesive material thereof. An adhesive layer of this typecan create non-uniform electrical transmission, provide lowerconductivity, require a high cost for manufacture, be difficult tomanufacture, have lower adhesivity, and be unable to absorbperspiration, with there being a tendency to lose adhesion if only aslight amount of moisture is present. The Kater patent discloses thatthe adhesive thereof is suitably PVP-based. The Goodman et al patent isconcerned with an electrolyte composition comprising an aqueous solutionof sodium chloride that is preferably completely saturated with silverchloride and that contains up to 7.5% polyvinyl alcohol as a thickeningagent. It is said that borax may be used to aid the polyvinyl alcohol inits thickening action.

Other patents pertaining to chemically cross-linking an aqueous solutionof a polymeric material include U.S. Pat. No. 3,087,920 to Suzumura etal, U.S. Pat. No. 4,036,808 to Rembaum et al, U.S. Pat. No. 3,932,311 toCaldwell et al, U.S. Pat. No. 2,616,818 to Azorlosa, U.S. Pat. No.4,089,832 to Yamauchi et al, U.S. Pat. No. 3,220,960 to Wichterle, U.S.Pat. No. 3,545,230 to Morse, U.S. Pat. No. 3,336,129 to Herrett et al,and U.S. Pat. No. 2,838,421 to Sohl. The Suzumura et al patent isconcerned with a cold water-soluble polyvinyl alcohol that includes anadmixture of partially saponified polyvinyl alcohol having a hydrolysisof 75-90%, a diaminostilbene optical bleaching agent, and a surfactant.At column 3, lines 33-35, of this patent, it is stated that in water,the partially saponified polyvinyl alcohol reacts with thediaminostilbene to form a three-dimensional bridge, thereby assuming agel form, and at column 3, line 47, the cold water-soluble polyvinylalcohol is stated to be useful as an adhesive.

The Rembaum et al patent relates to a conductive hydrogel formed byreacting the cationic polyelectrolyte thereof with a gel-forming polymersuch as polyvinyl alcohol, polyacrylic acid or a polyether. At column 8,lines 19-22, it is explained that a cross-linked hydrogel can beprepared from aqueous solutions of a mixture of polyvinyl alcohol andpolyacrylic acid or polyhydroxyethylmethacrylate. The gels of thispatent appear to be adhesive.

The Caldwell et al patent is concerned with an electrically conductingadhesive composition containing a cross-linked acrylate and/ormethacrylate polymer and silver particles. The Azorlosa patent relatesto a process for preparing a coated paper in which polyacrylamide or acopolymer of acrylamide and acrylic acid is used as an adhesive. In apreferred embodiment, the coated paper is treated with a cross-linkingagent so as to render the adhesive highly insoluble and stronglyadhesive.

The Yamauchi et al patent pertains to a water-containing plasticcomposition that contains a water-containing powdery gel obtained bysubjecting a water-soluble polymer such as polyvinyl alcohol,polyacrylamide or PVP to a cross-linking reaction and then pulverizingthe cross-linked product. Ionizing radiation can be used to effect thecross-linking. The plastic composition is suitable for manufacturingpoorly combustible molding materials.

The Wichterle patent is concerned with a hydrogel essentially consistingof a cross-linked hydrophilic polymer and 20-97% of an aqueous liquid.The hydrogel can be made, cut, or otherwise shaped to produce, forexample, a lens, a pessary, or a dialyzer diaphragm. Medicinally activeagents such as antibiotics may be dissolved in the aqueous constituentto provide medication over an extended period.

The Morse patent relates to a flexible cooling device comprised of areinforced layer of an insoluble hydrophilic gel. If desired, the gelcan include materials to control the physical and chemical propertiessuch as freezing point and chemical stability. Exemplary startingmaterials for preparing the gel include poly(ethylene oxide), PVP,polyacrylamide, polyvinyl alcohol, maleic anhydride-vinyl ethercopolymers, polyacrylic acid, ethylene-maleic anhydride copolymers,polyvinyl ether, polyethyleneimine, polyvinyl alkyl pyridinium halides,and polymethacrylic acid. Insolubilization can be effected by ionizingradiation or chemical cross-linking. The gel must be capable ofretaining relatively large quantities of a liquid. Water can be employedas the sole liquid, other liquids such as alcohols can be used, ormixtures of water and other liquids or solutes can be employed. When itis desirable to use more than one gel layer, a thin film of an inertmaterial such as polyethylene or a metal foil is used to separate thegel layers and thereby effectively prevent adhesion of the layers whenstacked.

The Herrett et al patent pertains to a plant growth medium containing anactive agent and a water-insoluble, cross-linked polymeric material thatserves as a matrix for the active agent. The polymeric material isillustratively polyvinyl alcohol, PVP, polyacrylic acid, polyvinylacetate, polyacrylamide, and a copolymer of vinyl alcohol and vinylacetate. The polymeric material is cross-linked either chemically or byionizing radiation. Irradiation is carried out in the solid phase or insolution using water, for example, as the solvent. In one embodiment, ahomogeneous water solution of the polymeric material is prepared andthen irradiated for a period of time sufficient to cause the formationof a gel-like material, and the gel-like material is dewatered.Exemplary active agents are quaternary ammonium salts, copper sulfate,antibiotics and propylene glycol insect repellants. At column 10, lines39-44, it is said that the roots of plants grown in soil formulationscontaining the cross-linked poly(ethylene oxide) of Herrett et al hadadhered thereto particles of the polymeric matrix.

The Sohl patent is concerned with an adhesive tape having awater-soluble adhesive composition that is essentially a blend of asolid water-soluble polyvinyl carboxylic acid such as polyacrylic acid,and a compatible hydroxy-polyalkylene permanent elasticizer such aspolyethylene glycol or polypropylene glycol. Another exemplary polyvinylcarboxylic acid is a 50/50 copolymer of polyvinyl methyl ether andmaleic anhydride. Internal strength of the adhesive is increased byincluding in the adhesive mixture a chemical cross-linking agent. Thecured type of adhesive is said to be more resistant to water but todissolve in water when mechanically agitated or mixed.

Other prior art patents that in addition to the Morse and Herrettpatents discussed above, pertain to a hydrogel based uponN-vinyl-2-pyrrolidone include U.S. Pat. No. 3,878,175 to Steckler, U.S.Pat. No. 3,759,880 to Hoffmann et al and U.S. Pat. No. 4,226,247 toHauser et al. The Steckler patent is concerned with a highly spongypolymeric material characterized by swelling in water and being softwhen wet. This spongy polymer is prepared by simultaneouslycopolymerizing and partially cross-linking 30-90 weight percent of anN-vinyl lactam monomer and 10-70 weight percent of an acrylate monomer.The spongy material is said to be adaptable for industrial applications,human use in toiletry, and as a sterile surgical dressing for sponging,wiping, or absorbing pus, blood and other body fluids during surgicaloperations. The Hoffman et al patent relates to the manufacture ofinsoluble and only slightly swellable poly-N-vinylpyrrolidone-2. Thepolymeric material of this patent is said to be a valuable absorbant formany purposes, especially as a beverage clarifying agent. The Hauser etal patent relates to an electrode having an adhesive that is preferablyPVP-based. The adhesive is compounded by mixing with an active agentsuch as PVP, a plasticizer such as dioctyl phthalate, camphor orglycerin, and, alternatively, a conventional tackifier.

The Herrett et al, Yamauchi et al and Morse patents, discussed above,describe the use of radiation to cross-link a polymeric material.Similarly, U.S. Pat. No. 3,897,295 to Dowbenko, U.S. Pat. No. 3,264,202to King, U.S. Pat. No. 2,964,455 to Graham, U.S. Pat. No. 3,841,985 toO'Driscoll et al, and U.S. Pat. No. 4,115,339 to Restaino pertain to theirradiation of polymeric materials.

In the Dowbenko et al patent, a solventless or nearly solventlesssolution of a polymer in a monomer is irradiated. The King patentpertains to forming a gel-like material by treating polymers of ethyleneoxide with radiation. The gel-like material of this patent is said tohave utility as a humidifier.

The O'Driscoll et al patent is concerned with irradiation of a solid,dry material containing PVP, and the Graham patent relates to the use ofirradiation to modify solid articles made from polymeric alkylene oxidesand polyvinyl ethers. At column 3, lines 59-61 of the Graham patent, itis disclosed that a benzene-soluble polytetramethylene oxide was soakedin water prior to irradiation. In the Restaino patent, an aqueoussolution of a water-soluble vinyl monomer is irradiated for the purposeof forming high molecular weight water-soluble polymers.

I believe this prior art and the other prior art of which I am aware,fails to provide a novel water-insoluble, hydrophilic, elastomeric,pressure-sensitive adhesive that is transparent, ultraconformable and asoft, but strong, rubber-like solid that will absorb moisture thatcannot be squeezed out; that will transmit oxygen, moisture, and drugsor salts soluble in the adhesive; and that will serve as a barrier tobacteria.

This adhesive could be useful as a coating on a supportive web-likesubstrate. The adhesive-coated web-like substrate could be used as abandage, a burn or wound dressing, an ostomy device, a decubitus ulcerpad, a sanitary napkin, a diaper, a vibration or impact absorbingmaterial such as a padding in shoes, splints, casts and orthopedicdevices or an athletic padding, a sound absorbing material, or a mediumfor delivering a pharmacologically active agent. Additionally, aself-supporting layer of this adhesive could serve these same uses, andfurthermore be useful as a cosmetic face mask and to secure a prosthesisor article of apparel to a mammalian body. One type of the noveladhesive could be electroconductive and function to attach anelectrically conductive member of an electrode to a selected surfacesuch as mammalian tissue.

DISCLOSURE OF THE INVENTION

It is accordingly one object of the present invention to provide a novelwater-insoluble, hydrophilic elastomeric, pressure-sensitive adhesive.This adhesive absorbs moisture that cannot be squeezed out; istransparent, ultra-conformable, and a soft, yet strong, rubber-likesolid that serves as a barrier to bacteria; and transmits oxygen,moisture, and drugs or salts soluble in the adhesive.

A further object is to provide a supportive, web-like substrate coatedwith the adhesive.

A still further object is to provide a bandage, a wound or burndressing, a sanitary napkin, a diaper, an ostomy device, a decubitusulcer pad, a vibration or impact absorbing material, a sound absorbingmaterial, and a medium for delivering a pharmacologically active agenthaving a layer of the adhesive supported by a web-like substrate.

An even further object is to provide a self-supporting layer of theadhesive that will serve these same uses, and furthermore be useful as acosmetic face mask and to secure a prosthesis or article of apparel to amammalian body.

A still further object is to provide a method for using theself-supporting layer of the adhesive for securing a prosthesis orarticle of apparel to a mammalian body.

A yet further object is to provide a method of making the adhesive.

An additional object of the present invention is to provide an adhesiveof this type that is electroconductive and useful for attaching anelectrically conductive member of an electrode to a selected surfacesuch as mammalian tissue.

An even additional object is to provide an electrode having a layer ofsuch an adhesive.

Another object is to provide a transcutaneous electric nerve stimulationelectrode, an electrosurgical return electrode or an EKG monitoringelectrode having a layer of such an adhesive.

Yet another object is to provide a method of adhering an electrode tomammalian tissue that includes contacting the tissue with an electrodeof this type.

Other objects and advantages of the present invention will becomeapparent as the description thereof proceeds.

In satisfaction of the foregoing objects and objectives, there isprovided by this invention a water-insoluble, hydrophilic, elastomeric,pressure-sensitive adhesive that includes at least one irradiationcross-linked synthetic organic polymer and an adhesive plasticizer. Theadhesive plasticizer is present in an amount sufficient to maintain theelastomeric state of the adhesive. The cross-linked polymer iswater-insoluble, has a three-dimensional matrix, and is formed from asolution or dispersion of at least one suitable gel-forming,uncrosslinked, synthetic organic polymer in a solubilizing plasticizer.The solubilizing plasticizer is irradiation cross-linking compatible,and the relative proportions of the uncrosslinked polymer and thesolubilizing plasticizer are such that the gel formed upon irradiationcross-linking, retains the solubilizing plasticizer within thethree-dimensional matrix. The plasticizers are the same or different,and include at least one substantially non-volatile elasticizer. Theelasticizer is present in an amount sufficient to maintain adhesivitywhen the adhesive plasticizer is substantially the elasticizer. Theadhesive is useful as a coating on an adhesive-supporting, web-likesubstrate, and is also useful as a self-supporting layer.

Also in satisfaction of the foregoing objects and objectives, there isprovided by this invention a conductive, water-insoluble, hydrophilic,elastomeric pressure-sensitive adhesive. This adhesive includes at leastone irradiation cross-linked synthetic organic polymer, aconductivity-enhancing amount of at least one conductivity-enhancingmaterial, and an adhesive plasticizer. The adhesive plasticizer ispresent in an amount sufficient to maintain the elastomeric state of theadhesive. The cross-linked polymer is water-insoluble, has athree-dimensional matrix, and is formed from a solution or dispersion ofat least one suitable gel-forming, uncrosslinked synthetic organicpolymer in a solubilizing plasticizer. The solubilizing plasticizer isirradiation cross-linking compatible, and the relative proportions ofthe uncrosslinked polymer and the solubilizing plasticizer are such thatthe gel formed upon irradiation cross-linking, retains the solubilizingplasticizer within the three-dimensional matrix. The plasticizers arethe same or different, and include at least one substantiallynon-volatile elasticizer. The elasticizer is present in an amountsufficient to maintain adhesivity when the adhesive plasticizer issubstantially the elasticizer. Also provided by the present invention isan electrode that includes an electrically conductive member and theelectro-conductive adhesive. Furthermore, in accordance with the presentinvention, there is provided a method of adhering an electrode tomammalian tissue that includes contacting the tissue with thiselectrode.

BRIEF DESCRIPTION OF THE DRAWING

Reference is hereby made to the accompanying drawing, which forms a partof the specification of the present invention.

FIG. 1 shows an electrosurgical return electrode (with certain areas cutaway) having a layer 14 of an electroconductive, water-insoluble,hydrophilic, elastomeric, pressure-sensitive adhesive, with a portion ofrelease liner 28 peeled back for attaching to arm 16.

FIG. 2 depicts a supportive web-like substrate 18 with a layer 20 of awater-insoluble, hydrophilic, elastomeric pressure-sensitive adhesivecoated thereon.

FIG. 3 shows a self-supporting layer 36 of the adhesive of FIG. 2.

BEST MODE FOR CARRYING OUT THE INVENTION

As discussed above, the present invention pertains to a novelpressure-sensitive adhesive. This adhesive is a water-insoluble,hydrophilic, elastomeric, pressure-sensitive adhesive; is a soft, yetstrong, rubber-like solid; and is further characterized by beingtransparent and ultraconformable. In fact, my adhesive has much higherdrape than the skin itself. My adhesive absorbs moisture that cannot besqueezed out, transmits oxygen, moisture, and drugs or salts soluble inthe adhesive, and functions as a barrier to bacteria.

My adhesive adheres aggressively to skin but does not appear to stickwell to hair, thus eliminating or greatly reducing the discomfort thatfrequently accompanies removal of a pressure-sensitive adhesive coatedsubstrate from an area of human body having hair present. My adhesivecan be left on the human body several hours or even days, anddiscoloration and wrinkled appearance of the skin does not result.

My adhesive can absorb a significant amount of moisture withoutsignificant reduction in adhesion, and in this regard will absorb ortransmit perspiration as it leaves the skin surface including moisture,salt, urea, ammonia and other waste products. My adhesive can beprepared to contain a significant amount of water, or can be prepared ina dehydrated state and thus have even greater capability for absorbingmoisture. My "dry" adhesive, as illustrated in Example 1 and Table 1,has unexpected high oxygen permeance (the meaning of the term "dry" isexplained below). The presence of a significant water phase in theadhesive is expected to produce even higher oxygen permeability.

In most embodiments, my adhesive is suberabsorbant. By superabsorbant, Imean that the adhesive will absorb an amount of water equal toapproximately its own weight, without a loss in adhesivity. Exemplaryembodiments in which the adhesive is not superabsorbant exist when theplasticizer is substantially 2 ethyl, 1-3 hexanediol or triethylcitrate, or mixtures thereof. In most of the uses for the adhesive setforth in this description of my invention, it is advantageous that theadhesive is superabsorbant. However, when used as an ostomy adhesive orpossibly when used as a drug delivery medium (depending on thesolubility characteristics of the drug), the adhesive should beabsorbant, not superabsorbant, and thus plasticizers of the type justmentioned should be used.

My adhesive will filter out microorganism contaminants by presenting atortuous path for the influx of the bacteria. As a result, antibioticsin a wound dressing may be unnecessary in most cases. My adhesive soclosely matches the fluid transmission and bacteria barriercharacteristics of human skin as to be like an instantly healing injuryas far as infection is concerned. It is believed that scar tissueformation would be retarded.

In one embodiment, the adhesive is electroconductive and is particularlysuitable for use with an electrode. Referring to FIG. 1, there isillustrated an electrosurgical return pad 10 that includes aconventional electrically conductive member 12 and an electroconductive,water-insoluble, hydrophilic, elastomeric, pressure-sensitive adhesive14, in accordance with the invention. Also shown in this Figure is anarm 16, which serves as a surface to which electrosurgical return pad 10is attached.

Referring to FIG. 2, there is shown a bandage 17 having a supportiveweb-like substrate 18 and an adhesive layer 20, in accordance with theinvention, coated thereon. This general structure is typical of abandage, sanitary napkin, burn or wound dressing, ostomy device,decubitus ulcer pad, diaper, a vibration or impact absorbing materialsuch as a padding, a sound absorbing material, and a medium fordelivering a pharmacologically active agent, in accordance with theinvention. However, the size and thickness of substrate 18 and adhesivelayer 20 will vary depending upon the use selected.

Also shown in FIG. 1 are foam layers 22 and 23, non-woven fabric layer24, adhesive layers 26 and 27, release liners 28, 30 and 32, andelectrical connection holes 34. These aspects of the pad areconventional. Adhesive layer 26 serves to bond fabric layer 24 to foamlayer 22. Foam layer 22 is conveniently a polyethylene foam, and fabriclayer 24 is suitably a polyester material such as Nexus® polyestermaterial sold by Burlington. Pad 10 is attached to arm 16 after releaseliner 28 is removed.

Pad 10 is advantageously manufactured in part by coating foam layer 22with adhesive layer 26, laying down fabric layer 24 on the adhesive toform a laminate, placing conductive member 12 on fabric layer 24,applying a solution or dispersion of an uncrosslinked, appropriatesynthetic organic polymer in a suitable plasticizer to fabric layer 24and conductive member 12, and subjecting the resulting laminate toionizing radiation. Release liner 28 is then put into place. Thesynthetic organic polymer and plasticizer are described below.

Referring to FIG. 3, there is shown a self-supporting layer 36 of theadhesive of the present invention. This general structure is typical forall uses of the adhesive as a self-supporting layer. However, the sizeand thickness of layer 36 will vary depending upon the use selected.Preferably, a self-supporting layer of the adhesive ranges in thicknessfrom about 3-6 mm. When prepared for use as a self-supporting layer, theadhesive layer, of course, could be sandwiched between a pair ofconventional release liners.

My adhesive includes at least one irradiation cross-linked syntheticorganic polymer and a sufficient amount of an adhesive plasticizer tomaintain the elastomeric state of the adhesive. The cross-linked polymeris formed by dispersing or solubilizing at least one suitablegel-forming, uncrosslinked synthetic organic polymer in a plasticizerthat has a composition the same as or different than the adhesiveplasticizer, and then subjecting the resulting solution or dispersion toan appropriate dosage of irradiation. Use of an appropriate dosage ofirradiation produces an adhesive with the properties described herein.The cross-linked polymer of the adhesive is water-soluble and has athree-dimensional matrix.

Conveniently, the uncrosslinked synthetic organic polymer includesrepeating units derived from a carboxy vinyl monomer, a vinyl estermonomer, an ester of a carboxy vinyl monomer, a vinyl amide monomer, ahydroxy vinyl monomer, a cationic vinyl monomer containing an amine or aquaternary ammonium group, or an N-vinyl lactam monomer. Alternatively,the uncrosslinked polymer is conveniently a homopolymer or copolymer ofa polyvinyl ether, or a copolymer derived from a half ester of maleicanhydride. A polymer formed from a compatible monomer mixture may beused such as a polymer formed from a mixture of an N-vinyl lactammonomer and an ester of a carboxy vinyl monomer. Also, compatibleuncrosslinked polymers may be used, in appropriate amounts, such asabout 11.25 weight percent polyvinyl alcohol (88% hydrolyzed) and about3.75 weight percent polyacrylic acid having a molecular weight of about450,000. Advantageously, the uncrosslinked polymer is water-soluble, andincludes, for example, repeating units derived from a carboxy vinylmonomer, is a homopolymer or copolymer of a polyvinyl alcohol, or is acopolymer formed from approximately substantially equal amounts ofmethyl vinyl ether and maleic anhydride.

Preferably, the uncrosslinked polymer includes repeating units derivedfrom an N-vinyl lactam monomer. Illustrative N-vinyl lactam monomers areN-vinyl-2-pyrrolidone, N-vinyl-ε-caprolactam and mixtures thereof. TheN-vinyl lactam monomer is suitably either a homopolymer ofN-vinyl-2-pyrrolidone, or a copolymer of N-vinyl-2-pyrrolidone and atleast one vinyl monomer that is compatible with solubility ordispersability of the uncrosslinked copolymer in the solubilizing ordispersing plasticizer and that is compatible with solubility ordispersability of the cross-linked copolymer in the adhesiveplasticizer. Vinyl monomers of this type include vinyl acetate, and anester of an α,β-olefinically unsaturated carboxylic acid and an aminogroup-containing alcohol. When the vinyl monomer is vinyl acetate, themole ratio of vinyl acetate and N-vinyl-2-pyrrolidone is advantageouslysuch that the copolymer is water-soluble.

A copolymer of N-vinyl-2-pyrrolidone and the carboxylic acid ester ispreferred, with the copolymer suitably containing mole percent of theester. It is particularly preferred for the ester to be eitherdimethylaminoethyl methacrylate or the partially or fully quaternizedsalt of this methacrylate. A partially quaternized salt-containingcopolymer of N-vinyl-2-pyrrolidone (having a K value of approximately90) is sold as a 20% aqueous solution under the trademark Gafquat 755 N.This commercially available copolymer contains 20 mole percent ofdimethylaminoethyl methacrylate partially quarternized with diethylsulfate. An advantageous polyvinyl pyrrolidone is K-90 PVP, and isavailable from GAF as Type NP-K90.

For purposes of this specification, the term "carboxy vinyl monomer"includes a water-soluble salt of a carboxy vinyl monomer with, forexample, an alkali metal, ammonia or an amine. Exemplary carboxy vinylmonomers include acrylic acid, methacrylic acid, crotonic acid,isocrotonic acid, itaconic acid and anhydride, a 1,2-dicarboxylic acidsuch as maleic acid or fumaric acid, maleic anhydride, and mixturesthereof. Conveniently, the carboxy vinyl monomer is acrylic acid.

When the carboxy vinyl monomer is a 1,2-dicarboxylic acid or maleicanhydride, the uncrosslinked polymer includes a comonomer. The comonomeris, for example, a C₂ -C₄ olefinic monomer such as ethylene, propylene,n-butylene or isobutylene; a C₄ diolefinic monomer such as butadiene; aC₁ -C₄ alkyl vinyl ether such as methyl vinyl ether; styrene; or vinylacetate. The amount of the 1,2-dicarboxylic acid or maleic anhydride issubstantially equivalent, on a molar basis, to the amount of thecomonomer. Vinyl acetate is a suitable comonomer in an amount up to asmuch as about 20 weight percent, with any of the other carboxy vinylmonomers.

As the polyvinyl alcohol, one or more water-soluble polyvinyl alcoholsare used. A convenient polyvinyl alcohol is a high molecular weight, 88%hydrolyzed polyvinyl alcohol prepared through hydrolysis of polyvinylacetate. This polyvinyl alcohol is commercially available as Gelvatol®20-90 and is a product of Monsanto.

The irradiation cross-linked polymer is produced by carrying out theirradiation on a solution or dispersion of the suitable gel-forming,uncrosslinked synthetic organic polymer in a plasticizer that iswater-soluble or water-dispersible, into which the uncrosslinked polymercan be dissolved or dispersed, and into which water and theuncrosslinked polymer can be dissolved or dispersed. The term"solubilizing plasticizer" is used in this description to designate thisplasticizer. This plasticizer is irradiation cross-linking compatible.For purposes of this specification, the term "irradiation cross-linkingcompatible" means that the solubilizing plasticizer does not inhibitirradiation-caused cross-linking of the polymer.

The solubilizing plasticizer includes at least one substantiallynon-volatile elasticizer, and conveniently includes a volatile solventthat in combination with the elasticizer serves to disperse or dissolvethe polymer. The volatile solvent is either aqueous, non-aqueous, or amixture, and is selected in conjunction with the elasticizer to form aplasticizer composition into which the uncrosslinked polymer can bedissolved or dispersed, and to form an adhesive plasticizer that willdissolve or disperse the cross-linked polymer. Conveniently, thevolatile solvent is aqueous, and it is especially convenient for thevolatile solvent to be water. When the volatile solvent is water, up toabout 90% of the solubilizing plasticizer may be water. A very importantfeature that separates my unique adhesive from the prior art is thatcertain formulations retain its adhesivity upon removal of the volatilesolvent. In contrast, an aqueous solvent gel such as disclosed bySteckler, Herrett et al, and Kater will become hard and non-adhesiveupon removal of the volatile solvent.

The substantially non-volatile elasticizer is present in an amountsufficient to maintain adhesivity of the cross-linked polymer-containingadhesive when the adhesive plasticizer is substantially made up of theelasticizer. By "substantially" in reference to the plasticizer is meantthat only as much as about 2 weight percent of the volatile solvent ispresent. Advantageously, the elasticizer is present in an amount rangingfrom about 0.5 to 4:1, on a weight basis, of the cross-linked polymer.

The solution or dispersion formed from combining the uncrosslinkedpolymer with the solubilizing plasticizer is either clear or hazy inappearance. The relative proportions of the uncrosslinked polymer andthe plasticizer are such that the gel formed upon irradiationcrosslinking, retains this plasticizer within the three-dimensionalmatrix.

Conveniently, the substantially non-volatile elasticizer is a suitablepolyhydric alcohol, mono- or diether of a polyalkylene glycol, mono- ordiester of a polyalkylene glycol, imidazoline derivative amphotericsurfactant, lactam, N-substituted lactam, amide, polyamide, amine,polyamine, condensate of polyethylene imine with epichlorohydrin,polyquaternary ammonium compound or compatible mixture thereof. Thepolyhydric alcohol is used with particular advantage, and it is veryadvantageous that the polyhydric alcohol is a polyalkylene glycol, inparticular a polyethylene glycol. Other useful polyhydric alcoholsinclude sorbitol, 1,3-butane diol, 1,4-butane diol, 1,4-butene diol, asuitable corn sugar derivative, pentaerythritol, trimethylolethane,glycerine, propylene glycol, 1,3-propane diol, polyglycerine, ethyleneglycol, and compatible mixtures. It is necessary that the elasticizerpresent during the irradiation treatment step is irradiationcross-linking compatible. Thus, for example, glycerine, which tends toreduce the effectiveness of irradiation cross-linking, should not bepresent as the elasticizer prior to irradiation treatment in an amountgreater than about 5% of the total formula weight, depending upon thepolymer upon which the adhesive is based. This amount of glycerine canbe present as the elasticizer and can accordingly be added to theelasticizer, once the cross-linking step has been completed. It is to beunderstood that, if, for example, the elasticizer is the amide or amine,the amide or amine is substantially non-volatile. Also, as explainedbelow, the elasticizer is typically a liquid at room temperature.

Once the irradiation treatment is completed, another way of altering thecomposition of the adhesive plasticizer in those cases in which thisplasticizer contains a volatile solvent, is to remove some of thevolatile solvent. When the volatile solvent is water, it is preferableto remove some of the water so that only a small amount, say up to about5%, of water is present as part of the adhesive plasticizer. In fact, itis even more preferable to remove a sufficient amount of water so thatthe adhesive is "dry", as defined below. An advantage of these dewateredadhesives is their capability for greatly increased moisture absorption.Additionally, as shown in the Examples, the dewatered or "dry" adhesiveis superior in its adhesivity to the "wet" adhesive, has markedlysuperior water vapor transmission, and has unexpectedly high oxygenpermeance. By "dry", for purposes of this specification, is meant thatan adhesive has a degree of dryness that is minimally that produced byallowing an adhesive to air dry for about 48 hours at approximately 30%relative humidity and 20° C. By "wet", for purposes of thisspecification, is meant that the adhesive contains at least about 55%water.

Generally, as noted above, the elasticizer is a liquid at roomtemperature. However, it is possible for the elasticizer to be a solidat room temperature when a freezing point depression results from thecombination of the elasticizer with the uncrosslinked polymer, someother component of the solubilizing plasticizer, or a suitable additivematerial that is placed into the formulation prior to the cross-linkingstep. A material that is normally solid but that experiences freezingpoint depression in the presence of an appropriate uncrosslinked polymersuch as polyacrylic acid having a molecular weight of approximately450,000, is a polyethylene glycol having a molecular weight from about600 to about 20,000. Particularly advantageous polyethylene glycols, foruse in my invention, have a molecular weight of about 300 or about 600.A polyethylene glycol (PEG) having a molecular weight of 300 is sold byUnion Carbide under the trademark Carbowax 300, and a PEG having amolecular weight of 600 is sold under the trademark Carbowax 600. It isalso possible for an elasticizer that is solid at room temperature to beused, if the remainder of the plasticizer composition is capable ofsolubilizing or dispersing both a mixture of this and the uncrosslinkedpolymer, and a mixture of this and the cross-linked polymer.

As discussed, the elasticizer is illustratively the polyhydric alcohol,the mono- or diether of a polyalkylene glycol or the N-substitutedlactam. It is very advantageous when the polyhydric alcohol is apolyalkylene glycol, with polyethylene glycol, polypropylene glycol andthe copolymer of ethylene oxide and propylene oxide being exemplary ofpolyalkylene glycols. A mono- or diether of polyethylene glycol issuitably the mono- or diether of a polyalkylene glycol, and apolyethoxylated fatty alcohol, polyethoxylated nonyl phenol or apolyethoxylated octyl phenol is conveniently the monoether of thepolyethylene glycol. Illustrative N-substituted lactams includeN-isopropyl-2-pyrrolidone, N-(N,N-dimethylamino)propyl-2-pyrrolidone,and N-cyclohexyl-2-pyrrolidone.

Suitably, the uncrosslinked polymer includes repeating units derivedfrom a vinyl amide monomer. A particularly suitable monomer of this typeis an amide of a α,β-olefinically unsaturated carboxylic acid, withacrylamide and dimethylaminopropyl methacrylamide being exemplary.Another amide of this type is methacrylamidopropyl trimethylammoniumchloride.

As explained earlier, it is advantageous for the uncrosslinked polymerto include repeating units derived from a carboxy vinyl monomer. Whenthe carboxy vinyl monomer is acrylic acid, the polymer may be acopolymer of acrylic acid and ethylene, vinyl acetate or an acrylateester. With this copolymer, there is included an amount of a basesufficient to solubilize the polymer, with the base being an amine, aquaternary ammonium or an alkali metal hydroxide. When the carboxy vinylmonomer is maleic acid, an advantageous comonomer is methylvinyl ether,ethylene, vinyl acetate, styrene or butadiene, with the amount of thecomonomer being substantially equivalent, on a molar basis, to theamount of the maleic acid. When the comonomer is styrene or vinylacetate, there is included enough of a base sufficient to solubilize thecopolymer.

An adhesive in accordance with my invention prepared from anuncrosslinked polymer or plasticizer that is skin irritating, or thatotherwise contains a skin-irritating additive is better employed so asnot to be in contact with skin. An exemplary polymer of this typepredominantly includes repeating units derived from a carboxy vinylmonomer such as acrylic acid, and an illustrative plasticizer contains asurfactant or detergent as the elasticizer. Otherwise, my adhesive hasthe substantial advantage of being hypoallergenic.

When the uncrosslinked polymer includes repeating units derived from anN-vinyl lactam monomer, particularly useful elasticizers include apolyethylene glycol, an imidazoline derivative amphoteric surfactant, apolyethoxylated fatty alcohol, a polyethoxylated fatty acid, apolyethoxylated nonyl phenol, and a polyethoxylated octyl phenol. Apolyethoxylated octyl phenol surfactant is sold under the Tritonbrandname by Rohm & Haas.

A convenient polyvinyl ether for use as the uncrosslinked polymerstarting material is polymethylvinyl ether or polyethyl vinyl ether.Particularly suitable elasticizers include the monoether of apolyalkylene glycol or the monoester of a polyalkylene glycol. Anillustrative monoether of a polyalkylene glycol is polyethoxylated octylphenol, and an exemplary monoester of a polyalkylene glycol is a fattyacid ester of polyethylene glycol such as polyethylene glycol 300monostearate. Other useful elasticizers include an N-substituted lactamand, of course, polyethylene glycol. An N-substituted lactam is also aparticularly convenient elasticizer for use with an uncrosslinkedpolymer derived from an N-vinyl lactam monomer.

When the uncrosslinked polymer includes repeating units derived from avinyl ester monomer, the polymer contains an amount of a secondcomonomer sufficient to make the polymer soluble or dispersible in theplasticizer prior to the irradiation treatment step, and also soluble inthe adhesive plasticizer. Exemplary vinyl esters include vinyl acetateand vinyl propionate, and the comonomer is illustratively anN-substituted lactam, a vinyl alcohol, a hydrolyzed maleic anhydride, orcrotonic acid. A copolymer containing the vinyl ester and vinyl alcoholmay be prepared through incomplete hydrolysis of the vinyl ester. Acopolymer of vinyl acetate and maleic anhydride is prepared throughhydrolysis and base treatment. When the comonomer is crotonic acid, asufficient amount of an appropriate base is added to dissolve thepolymer in the plasticizer prior to the irradiation treatment.Conveniently, this copolymer contains vinyl acetate and crotonic acid inan about 19:1 mole ratio.

When the uncrosslinked polymer is a copolymer derived from a half esterof maleic anhydride, the half ester is suitably the methyl half ester orthe ethyl half ester, and the comonomer is advantageously a C₁ -C₄ vinylether such as methyl vinyl ether, or ethylene.

Other exemplary vinyl amide monomers are prepared from anα,β-olefinically unsaturated carboxylic acid and a diamine such asdimethylaminoethylamine and aminoethyl trimethylammonium chloride.Illustrative hydroxy vinyl monomers, for use as the uncrosslinkedpolymer starting material, include hydroxyethyl acrylate andhydroxypropyl acrylate. Vinyl benzyl trimethylammonium chlorideexemplifies a cationic vinyl monomer containing an amine or a quaternaryammonium group.

As explained earlier, the relative proportions of the uncrosslinkedpolymer and the solubilizing plasticizer are such that the gel formedupon the irradiation cross-linking, retains this plasticizer within thethree-dimensional matrix. When the uncrosslinked polymer includesrepeating units derived from a carboxy vinyl monomer, a vinyl estermonomer, an ester of a carboxy vinyl monomer, a vinyl amide monomer, ahydroxy vinyl monomer, or a cationic vinyl monomer containing an amineor a quaternary ammonium group, the solution or dispersion to beirradiated conveniently contains about 5-50 weight percent of theuncrosslinked polymer. Also, when the uncrosslinked polymer is acopolymer derived from a half ester of maleic anhydride, the solution ordispersion advantageously contains about 5-50 weight percent of theuncrosslinked polymer. It is suitable for the solution or dispersion tocontain about 7-60 weight percent of the uncrosslinked polymer, in thecase that the uncrosslinked polymer includes repeating units derivedfrom an N-vinyl lactam monomer. When the uncrosslinked polymer is ahomopolymer or copolymer of a polyvinyl ether, it is convenient for thesolution or dispersion to contain about 5-60 weight percent of theuncrosslinked polymer. In the case where the uncrosslinked polymer is ahomopolymer or copolymer of a polyvinyl alcohol, the solution ordispersion to be irradiated advantageously contains about 5-30 weightpercent of the uncrosslinked polymer. When the uncrosslinked polymerincludes repeating units derived from a carboxy vinyl monomer, it isespecially suitable for the solution or dispersion to contain about14-20 weight percent of the uncrosslinked polymer, with about 20 weightpercent being preferred. When the uncrosslinked polymer includesrepeating units derived from an N-vinyl lactam monomer, it isparticularly advantageous for the solution or dispersion to containabout 12.5-22.5 weight percent of the uncrosslinked polymer, with about20 weight percent again being preferred. A particularly convenientconcentration of the uncrosslinked polymer in the solution or dispersionis about 7- 25 weight percent when the uncrosslinked polymer is ahomopolymer or copolymer of a polyvinyl alcohol, with about 10 weightpercent being preferred.

When the uncrosslinked polymer includes repeating units derived from acarboxy vinyl monomer, a particularly suitable ratio of the elasticizerto the carboxy vinyl monomer is an about 1:1 ratio, on a weight basis.When the uncrosslinked polymer is polyacrylic acid, the polyacrylic acidconveniently has a molecular weight of about 450,000-500,000.Polyacrylic acid having a molecular weight of about 500,000 is sold in a15% aqueous solution by B. F. Goodrich as Carbopol® Ex-17, andpolyacrylic acid having a molecular weight of 450,000 is sold asCarbopol®907. A particularly advantageous adhesive, as discussedearlier, is "dry". Removal of the volatile solvent to form this adhesiveis achieved as explained above, or by using equivalent techniques.

When the adhesive includes irradiation cross-linked K-90 polyvinylpyrrolidone and polyethylene glycol having a molecular weight of about300, it is highly preferred for the polyethylene glycol to be present inan amount that is about 0.75-1.5 times the amount, on a weight basis, ofthe polyvinyl pyrrolidone. These particular compositions and similarcompositions in which the polyvinyl pyrrolidone is a copolymer ofN-vinyl-2-pyrrolidone and vinyl acetate or either dimethylaminoethylmethacrylate or the partially quaternized salt of this methacrylate, arethe very preferred compositions of this invention.

The dosage of irradiation to produce my adhesive depends upon factorsthat include the concentration of the uncrosslinked polymer in thesolubilizing plasticizer, and the molecular weight of the uncrosslinkedpolymer. For instance, a relatively lower dosage of irradiation isrequired by a relatively higher concentration of the uncrosslinkedpolymer or a relatively higher molecular weight uncrosslinked polymer;whereas a relatively higher amount of irradiation is required by arelatively lower concentration of the uncrosslinked polymer or arelatively lower molecular weight uncrosslinked polymer. The choice ofelasticizer and the relative proportions of the elasticizer, theremaining plasticizer components, and the uncrosslinked polymer alsoaffect the dosage requirements.

In addition, when the irradiation is carried out at a relatively lowrate, and in the presence of a free radical scavenger such as oxygen,relatively higher dosages are required; whereas, when the irradiation iscarried out under conditions that favor the relatively long existence ofthe free radicals produced, as for example, when the irradiation iscarried out with a high dose rate, in the absence of oxygen, or insolution where oxygen is rapidly used up, a relatively lower dosage isnecessary.

The term "irradiation" as used herein, means high energy radiationand/or the secondary energies resulting from conversion of electron orother particle energy to neutron or gamma radiation. These energies areat least equivalent to about 100,000 electron volts. While various typesof irradiation are suitable for this purpose, such as X-ray and gammaand beta rays, the radiation produced by accelerated high energyelectrons is conveniently and economically applicable. However,regardless of the type of radiation and the types of equipment used forits generation or application, the ionization radiation need only beequivalent to at least about 100,000 electron volts.

While there is no upper limit to the electron energy that can be appliedadvantageously, the effects desired in the practice of this inventioncan be accomplished without having to exceed about 20 million electronvolts. Generally, the higher the electron energy used, the greater isthe depth of penetration into the structure of the materials to betreated, and the shorter is the time of exposure required. For othertypes of radiation, such as gamma and X-rays, energy systems equivalentto the above range of electron volts are desirable.

It is intended that the term "irradiation" include "ionizing radiation"which has been defined as radiation possessing an energy at leastsufficient to produce ions or to break chemical bonds and thus includes"ionizing particle radiation" as well as radiations of the type termed"ionizing electromagnetic radiation".

The term "ionizing particle radiation" has been used to designate theemission of electrons or highly accelerated nuclear particles such asprotons, neutrons, alpha-particles, deuterons, or beta-particles,directed in such a way that the particle is projected into the mass tobe irradiated. Charged particles can be accelerated by the aid ofvoltage gradients by such devices as accelerators with resonancechambers, Van der Graaff generators, betatrons, synchrotons, cyclotrons,dynamatrons and insulated core transformers. Neutron radiation can beproduced by bombarding a selected light metal such as beryllium withpositive particles of high energy. Particle radiation can also beobtained by the use of an atomic pile, radioactive isotopes or othernatural or synthetic radioactive materials.

"Ionizing electromagnetic irradiation" is produced when a metallictarget, such as tungsten, is bombarded with electrons of suitableenergy. This energy is conferred to the electrons by potentialaccelerators of over 0.1 million electron volts. In addition toirradiation of this type, commonly called X-ray, an ionizingelectromagnetic irradiation suitable for the practice of this inventioncan be obtained by means of a nuclear reactor (pile) or by the use ofnatural or synthetic radioactive material, for example, cobalt 60.

Dosages of irradiation ranging from about 0.5-7.5 megarads are usefulfor cross-linking the uncrosslinked polymer, with a dosage of about3.5-4.5 megarads being particularly suitable. Thus, this dosage range isespecially useful for a composition substantially containing about 18-22weight percent, K-90 polyvinyl pyrrolidone, about 10-70 weight percentpolyethylene glycol having a molecular weight of about 300, and water.The adhesive produced is a preferred adhesive, and can be madeelectro-conductive by including an appropriate amount of a conductivityenhancer such as about 6-8 weight percent. It is very preferred for thisadhesive to contain about 25-30 weight percent of PEG 300, and about 20weight percent PVP.

My adhesive optionally contains a compatible preservative such as methylparaben or propyl paraben. Mixtures of preservatives may be used, and,when used, a preservative is used in an amount sufficient to achieve apreservative effect. Also, my adhesive may contain a pigment such asultramarine blue.

My adhesive is useful as a coating on a supportive web-like substrate.As a result of high cohesion, and by a judicious choice of the web-likesubstrate so that there is a very high adhesion of the adhesive to thesubstrate, my adhesive does not leave behind an adhesive residue. Whenpolystyrene, for example, is used as the supportive substrate, very highadhesion of the adhesive to the polystyrene results if irradiation iscarried out with the solution or dispersion of the uncrosslinked polymerin direct contact with polystyrene.

A particular advantage of my adhesive is that it tends to bere-applicable. As a result, the adhesive may be re-positioned severaltimes without loss of adhesive performance.

My adhesive is elastomeric and undergoes elastic deformation. When myadhesive is strained, a restoring static stress develops. Even afterundergoing several hundred percent strain, there is little if anyvisually detectable permanent set, after relaxation of my adhesive. Myadhesive is very low in stiffness and has a modulus as low as gelatindesserts or even lower.

Since my adhesive is elastomeric and does not exhibit excessive coldflow, it is possible to produce my adhesive in a very thick layer form,even as great as about 40 mm or more. However, a layer having athickness of about 3-6 mm is preferable, especially when a layer of myadhesive is self-supporting, and has the advantage of allowingarticulation of a patient's body with a minimum of retriction and aminimum of painful pulling. A self-supporting layer of my adhesive couldbe a coating on a non-supportive thickness of a web-like substrate suchas gauze or a non-woven fabric. In this instance, the web-like substratewould function to increase dimensional stability and enable the adhesiveto be cut more easily.

A supportive web-like substrate coated with a layer of my adhesive has amultiplicity of uses, and the web-like substrate is selected accordingto the desired use. Suitably, the web-like substrate is non-conductive.A number of uses exist for the coated substrate such as a bandage, aburn or wound dressing, a sanitary napkin, an ostomy device, a diaper, adecubitus ulcer pad, a vibration or impact absorbing material, a soundabsorbing material, and a medium for delivering an adhesive-solublepharmacologically active agent. In certain of these uses, the adhesiveincludes a pharmacologically active agent that is soluble in theadhesive.

When used as a self-supporting layer, my adhesive has the uses describedabove for the coated substrate. A self-supporting layer of my adhesiveis also useful as a cosmetic face mask, and to secure a prosthesis or anarticle of apparel to a mammalian body.

When used in a bandage, my adhesive material is able to replace allthree parts of the bandage, that is, the adhesive, gauze and substrate,and may be the best material known for any of these three parts. As theadhesive part of the bandage, it is non-traumatic, does not pull hair,does not induce painful pulling in use, does not cause discomfort orinjury upon removal, and does not cause the skin-wrinkling moistureretention observed with many other adhesives. As a gauze material, myadhesive allows continual observation of a patient's condition withoutdisturbing the patient. Being a soft elastomer, it provides superiorpadding as well. Being nonfibrous, it does not strongly adhere to ascab, and usually will be removed without scab trauma. My adhesive willsignificantly reduce bacterial influx by filtering bacteria out. Beingelastomeric in nature, my adhesive can be used without a supportingsubstrate when an appropriate thickness is provided. Its superior drapewill allow it to conform to the most intricate body contours, remainingattached even during vigorous movement. Its high oxygen and moisturepermeability is most beneficial in bandage applications, particularly asa means of controlling anaerobic bacterial infection.

My adhesive can absorb the fluid exuded from a minor injury and thusserve as both adhesive and absorbant pad. A substantial advantage ofthis is that if an appropriately-sized sheet of adhesive-coatedsubstrate is available, one can cut a special size or shape of bandageto fit the exact need. This is in contrast to commercially availablebandages that are made of an absorbant pad secured to an adhesive tape,and that require providing a gauze pad of appropriate size and shape andalso an adhesive tape of appropriate size and shape.

When gauze is used to cover an injury site, a frequent problem is thatthe coagulated blood and body fluids tend to encapsulate the gauzefibers, as a result of which the gauze becomes adhered to the injurysite. In contrast, my adhesive is less likely to adhere to the injury.When used as a gauze replacement, my adhesive can be prepared to containan amount of moisture ranging from about zero to ninety percent so thatone can maintain either a high moisture environment or a low moistureenvironment over the area being treated.

As a burn dressing, it is believed my adhesive will function as anartificial skin graft that will stabilize a patient until grafts of hisown tissue are available.

When used as sanitary napkin, a layer of my adhesive can serve as allthree parts of the sanitary napkin, that is, as the absorbant material,the adhesive, and the supporting structural member. The ability of myadhesive to adhere to the contours of the vaginal area even duringvigorous movement, to absorb menstrual fluid, and to provide a seal overthe vaginal area makes this adhesive material an ideal sanitary napkin.An about 3/16" sheet of this material could be used alone, withoutsupport. When unsupported, the opposite side of the adhesive could havean undergarment adhesion-preventing coating provided, for example, bydusting this side with talc or treating it with a silicone fluid. Sincemay adhesive does not absorb particulates, it is advantageous to use apad of another absorbant material over the center portion of thesanitary napkin.

As a cosmetic face mask, my adhesive is soft enough to be comfortablyused over the entire face. Moisturizers could be added in an appropriateamount in order to provide an overnight beauty treatment which, beingcontinuous through the night, will provide a most effective "youthrestoring" beauty aid. Additionally, pharmacologically active agentssuch as those useful against acne or providing sunburn pain relief couldbe included in the adhesive.

When used as a delivery medium for a pharmacologically active agent, alayer of my adhesive can be applied to skin areas other than the face.This use is particularly advantageous when the pharmacologically activeagent is able to pass through the skin. In addition to applying myadhesive to the skin, my adhesive may be located in the vagina, rectumor mouth, and even under the skin for subcutaneous administration. In aninteresting use of my adhesive as a drug delivery medium, my adhesive isprepared so as to include an aqueous solution of epsom salt. A layer ofthe adhesive is applied to the feet, and the user is able to freely moveabout and still "soak" his feet. The adhesive will retain the epsom saltsolution, and even if compressed will not release moisture. Thepharmacologically active agent should be soluble in the plasticizerphase of the adhesive, and must be present in an amount sufficient tobring about the desired pharmacological effect. Exemplarypharmacologically active agents include hormones such as estrogen,analgesics, and antirheumatics. Additionally, the adhesive may be usedas a carrier for a depilatory agent.

My adhesive is especially useful as a vibration or impact absorbingmaterial such as a padding since it is very soft and can undergoconsiderable shear strain and yet not transmit very high stresses. Aself-supporting layer of the adhesive may be used as padding in shoes,orthopedic devices, casts and splints. In another use as a padding, alayer of the adhesive may be used as a saddle blanket so as to reducesaddle sores of horses. My adhesive is useful for attenuating vibrationin motion picture equipment, and in various sensitive instruments.Additionally, my adhesive provides good sound attenuation.

The properties of my adhesive result in usefulness for treating orpreventing bed sores or decubitus ulcers. This is accomplished byapplying a layer of my adhesive to a selected area of the body, as aresult of which rubbing of this area is reduced.

My adhesive may contain beneficial ingredients such as humectants, skinconditioners, depilatories, hormones, perfumes, cleansing agents, acnemedication, antiperspirants, astringents, sun screens, and artificialsun tanning materials. When used as medium for delivering anadhesive-soluble pharmacologically active agent, my adhesive mayfunction to provide continuous drug delivery by providing an appropriateconcentration of the drug in a suitable adhesive. In addition to thosedrug types set forth above, the drug could be nitroglycerin or a motionsickness treatment drug. In situations where it is desirable to have abacteriastatic agent in the adhesive, for example, where the adhesive isto be applied to the face of a person for treatment of acne or is to beapplied topically to the skin for treatment of a topical infection, myadhesive includes a quaternary ammonium compound. For treatment ofringworm, athlete's foot, jock itch or other topical fungal infections,an appropriate antifungal compound is added to my adhesive.

As a self-supporting layer, my adhesive may also be used to secure aprosthesis to a mammalian body. Also, an article of apparel may besecured to a mammalian body by use of a self-supporting layer of myadhesive.

In forming my adhesive, irradiation is used to induce cross-linking ofan appropriate synthetic organic polymer. The use of an irradiationprocessing technique enables in situ preparation of films and coatingsto be done continuously, and additionally enables bulk cross-linking,especially if gamma rays from cobalt 60 are used. Using irradiation tocross-link the synthetic organic polymer allows the use of high speedweb processing techniques and thereby results in high volume continuousproduction of adhesive-coated substrate. Simple liquid handlingequipment can be used to dispense the uncrosslinked formulation onto amoving web of substrate, which then passes under a scanning electronbeam.

One potential problem of a polymer that has been chemically cross-linkedmay exist in the situation where an ester linkage has been formed by thereaction of a carboxyl group of the polymer with an oxirane or aziridinegroup of the cross-linker, and a significant amount of water is present.In this instance, the ester linkage may not be hydrolytically stableover a period of several weeks. Similarly, an amide bond formed betweenthe carboxyl group of a polymer and the amine group of a cross-linkingagent may not be hydrolytically stable. On the other hand, thecarbon-carbon bonds formed between adjacent polymer molecules duringirradiation are very stable. Further advantages of using irradiation arehigh efficiency, ease of handling, and the elimination of potentiallytoxic chemicals. Irradiation is a clean process that is thought toimpart no residual chemical toxins. The advantages of easy handling andrapid processing equipment make the use of irradiation very costeffective. Cross-linking can be accomplished instantly rather thanrequiring prolonged cure cycles such as are required with an epoxy cure.A further advantage is that in certain instances when chemicalcross-linking is used, the cross-linked polymeric material would have tobe air dried to remove the water in order to convert the material from aflowable liquid state to a pressure-sensitive adhesive. In contrast, useof an appropriate dosage of irradiation would convert such a compositioninstantly to a pressure-sensitive adhesive.

A theoretical dose rate can be calculated for an electron beam by usingthe equation: ##EQU1## assuming an energy loss similar to water, where dis the dose in megarads, t is the time in minutes, A is the area of thescanning electron beam in space meters, I is the current inmilliamperes, and 1.1 is an empirical constant dependent upon thematerial being irradiated and a beam energy for 2 Mev. Using a scanningelectron beam of 152.4 cm scanning width and a scanning length of 5.08cm, and using current of 3-30 milliamperes, the theoretical dose rate iscalculated to be 2.5-25×10⁹ rads per hour. The material to be irradiatedis passed under the scanning beam on a moving conveyor. In thisinstance, the conveyor travels in the direction of the 5.08 cm scanningcoordinate so as to allow the conveyor to take advantage of the 152.4 cmwidth.

Using a 100 milliamp irradiation source, it may be possible to reachproduction rates as high as a million square feet per day. Since, inmost embodiments, a volatile organic solvent is not used in making myadhesive, solvent removal to produce a "dry" adhesive does notnecessitate expensive pollution control and explosion preventionequipment.

Under certain circumstances, a cross-linking promoter is advantageouslyadded to the solution or dispersion of the uncrosslinked polymer.Exemplary promoters include polymercaptans such as 2,2-dimercaptodiethylether, dipentaerythritol hexa(3-mercaptopropionate), ethylenebis(3-mercaptoacetate), pentaerythritol tetra(3-mercaptopropionate),pentaerythritol tetra(3-mercaptopropionate), pentaerythritoltetrathioglycolate, polyethylene glycol dimercaptoacetate, polyethyleneglycol di(3-mercaptopropionate), trimethylolethanetri(3-mercaptopropionate), trimethylolethane trithioglycolate,trimethylolpropane tri(3-mercaptopropionate), trimethylolpropanetrithioglycolate, dithioethane, di- or trithiopropane and 1,6-hexanedithiol.

In another emdobiment of my invention my adhesive is electroconductiveand useful for attaching an electrically conductive member of anelectrode to a selected surface such as mammalian tissue. Basically,this adhesive is the same adhesive as that discussed above except that aconductivity-enhancing material is included in the adhesive composition.Conveniently, the conductivity-enhancing material is added to thesolution or dispersion of the uncrosslinked polymer prior to theirradiation treatment step. Preferably, the conductivity-enhancingmaterial is a non-polymeric, ionizable organic or inorganic salt. Theamount of the conductivity-enhancer to be used in my adhesive dependsupon factors such as the conductivity-enhancing material selected, witha relatively smaller amount of a more conductive material beingrequired, and a relatively greater amount of a material providingrelatively less conductivity, being needed. Exemplary non-polymeric,ionizable organic or inorganic salts include ammonium sulfamate,monoethanolamine acetate, diethanolamine acetate, sodium lactate, sodiumcitrate, sodium chloride, magnesium sulfate, and polyethyleneglycol-soluble salts such as ammonium acetate, magnesium chloride andmagnesium acetate. About 5% of magnesium sulfate, about 5-7% ofmagnesium acetate or about 7% of ammonium acetate is suitably used asthe conductivity-enhancer in my adhesive. Mixtures ofconductivity-enhancing materials may be used. Thus, for example, amixture of magnesium chloride and magnesium acetate could be utilized.

My electroconductive adhesive is particularly suitable for use as anelectrode adhesive, and thus is conveniently used as a coating on anelectrically conductive substrate such as member 12 of FIG. 1.Electrically conductive members are well known in the electrode art.Thus, a discussion is not provided concerning such a member except topoint out that the selection of the particular material to be used toform the member, as well as selection of the size, shape and thickness,is dependent on the end use contemplated for the electrode. Generally,member 12 has a thickness ranging from about 15 thousandths up to about1/8 inch. As shown in FIG. 1, electroconductive adhesive 14 serves toattach member 12 to a surface 16. The electroconductivity of theadhesive promotes the transfer of electric signals between member 12 andsurface 16. Exemplary electrodes for attachment to mammalian skininclude a transcutaneous electrical nerve stimulation electrode, anelectrosurgical return electrode and an EKG monitoring electrode.

Examples of my invention will now be provided in order to illustrate theinvention. These examples are to be regarded as exemplary only. Allpercentages are weight percent unless otherwise indicated.

EXAMPLE 1

A solution coontaining 20% PVP, 25% PEG and 55% water was prepared, anda 1.5 mm coating of the solution was applied to one side of a whitepolyester cloth. The PVP was PVP K-90 sold by GAF, the PEG wasCarbowax®300 sold by Union Carbide, and the cloth is similar to thefabric customarily making up a nurse's uniform. A protectivepolyethylene film was applied to the coated fabric, and the sample wassubjected to an ionizing irradiation dose of 3.5 megarads using a 2.5Mev electron beam source. This procedure was repeated several times toproduce a number of samples. The polyethylene film was removed fromapproximately half of the samples, and these particular samples wereallowed to air dry for about 48 hours at approximately 30% relativehumidity and 20° C., to form "dry" samples. The "wet" and "dry? sampleswere then subjected to a rolling ball tack test, and tested for peelstrength and lap shear. The rolling ball tack test was conducted asfollows: A steel ball was rolled down an inclined trough of 8.3" lengthand having a cross-sectional width of 0.53 inches (the trough beinginclined at an angle of 21 degrees 30 minutes from the horizontal). Theadhesive sample was positioned so that as the ball rolled off the end ofthe trough, the ball began contacting the surface of the adhesivesample. A relatively lower number means the adhesive had a better tack.

The samples were tested for 180° peel as follows: A 4" length of aspecimen of 1" width was caused to adhere to one surface of avertically-oriented steel plate, the remaining length of the specimenwas doubled back, and the loose end of the remaining length wasanchored. The steel plate was pulled vertically upward at a speed of 6"per minute, and the force to strip the adhesive sample from thevertically oriented steel plate surface was measured.

Each sample was analyzed for 90° peel as follows: A 6" length of aspecimen of 1" width was caused to adhere to one surface of avertically-oriented steel plate and the remaining 6" length of thespecimen was caused to adhere to the top surface of a horizontallyoriented steel plate. The vertically oriented steel plate was movedvertically upward at a speed of 6" per minute, and the force to stripthe adhesive sample from the horizontal plate surface was measured. Thespecimens for the peel strength testing showed a wide variance inthickness within a given specimen type. Also, the specimens containedair bubbles.

In addition, the solution of PVP, PEG, and water was used to saturate apiece of gauze with about 1 mm of adhesive, and the saturated gauze wasplaced between two polyethylene sheets, and irradiated in like manner asbefore. This procedure was repeated to produce additional samples fortesting for water vapor transmission and oxygen permeance. Prior to thistesting, the upper layer of polyethylene was removed in the case ofabout half the samples, and these particular samples were allowed to airdry for about 48 hours at approximately 30% relative humidity and 20° C.to produce "dry" samples.

Oxygen permeance was measured as follows: An adhesive sample having anarea of 3.4 in² and a thickness of 0.15 inches was located between twochambers, with one side of the adhesive sample forming a portion of onechamber wall, and the other side of the sample forming a portion of theother chamber wall. Oxygen was flowed from a regulator through a gasflow meter into a reservoir connected to a manometer. A 1 psi O₂pressure difference was set up between the two chambers, and the oxygenpermeance is measured.

The results for the rolling ball tack test, peel strength test, lapshear test, and oxygen permeance are shown in Table 1. The water vaportransmission results are set forth in Table 2.

EXAMPLES 2-44

Adhesives in accordance with the invention, certain of which areconductive, were prepared using the formulations shown in Table 3. Ineach case, a solution or dispersion was formed, and a layer ranging fromabout 1-6 mm in thickness was subjected to a dose of a 2.5 Mev electronbeam radiation source, as indicated in the Table. The layer thicknessranged from about 1-3 mm for formulations containing PVP and PEG, andranges from about 2-6 mm for the other formulations, In each instance,the resulting cross-linked material was adhesive.

In addition, several of the cross-linked adhesives were allowed to airdry for about 48 hours at approximately 30% relative humidity and 20° C.For these particular formulations, the theoretical formula of thecorresponding dry adhesive is shown in the Table. In all cases, thecorresponding "dry" material was a good adhesive.

COMPARATIVE EXAMPLES 1-5

Following the procedure of Examples 2-44, a solution or dispersion ofeach of the formulations shown in Table 4 was prepared, and a layerranging in thickness from about 2-6 mm was subjected to a dose of 2.5Mev electron beam radiation, as indicated in this Table. In each case,the resulting cross-linked material was adhesive. Each of theseadhesives was allowed to air dry in the same manner as each of theadhesives of Examples 2-44 for which a theoretical formula of thecorresponding "dry" adhesive is shown. "Dry" comparative material 1 wasa non-adhesive brittle film, and the other four "dry" comparativematerials were non-adhesive flexible films.

EXAMPLE 45

A conductive adhesive was prepared using the following formulation:

    ______________________________________                                        Polyvinyl pyrrolidone (PVP K-90, GAF)                                                                 20%                                                   Polyethylene glycol 300 (Carbowax 300                                                                 25%                                                   Sentry Grade, Union Carbide)                                                  Magnesium Acetate (Reagent Grade,                                                                     7%                                                    J. T. Baker)                                                                  Methyl paraben (Inolex) .037%                                                 Propyl Paraben (Inolex) .012%                                                 FD & C Blue #2 (H. Kohnstamm)                                                                         .0012%                                                Water                   Balance                                               ______________________________________                                    

A 1/15 inch thick layer of the viscous liquid was applied to theelectrosurgical return electrode pad of FIG. 1. This pad had 20 squareinches of electrode area. The coated pad was then subjected to 3.5megarads of 2.5 Mev electron beam radiation.

The electrical impedance of the electrode was measured by constructing acircuit in which an electrical current was passed through the entirearea of the electrode. This was done by first securing the full surfaceof the electrode to a stainless steel plate. The stainless steel platewas then connected to the active electrode of a Valleylab SSE3-Belectrosurgical generator, while the electrode being tested was groundedto the generator ground. A Simpson radiofrequency ammeter was connectedin series with the electrode/stainless plate and a Fluke model 8920Atrue RMS voltmeter was connected between the steel plate and theelectrode. The SSE3-B generator was adjusted to produce a 750,000 hertzsine wave signal, and the current was adjusted to one amp using theSimpson ammeter as a reference. The voltage was read on the voltmeterand recorded. The result is shown in Table 5, as average impedance persquare inch.

The peel strength at 180° was tested using a steel plate, as in theTable 1 peel strength data, and was also tested using the skin of femaleand male human test subjects. The procedure used was essentially thesame as that set forth with respect to the 180° peel test of Table 1,except that the tensile tester was used to peel off the electrode at arate of 12 inches per second. Furthermore, in carrying out the test withhuman test subjects, the electrode pad was pulled off manually using ahand-held Ametek 0-30 pound scale. In each of these experiments, theelectrode pad was secured to the thigh of the test subject. Attentionwas invited to Table 6, which shows the results.

The adhesive of the electrode pad was tested for any irritating effectupon human subjects, with particular attention being given to discomfortupon removal, pulling of hair, edema, erythema, bruising and removal ofepidermis. The electrode pad was applied to the subject and removedwithin ten minutes, with the runs being uniformly carried out. The dataobtained is set forth in Table 7.

Electrical impedance of the electrode was tested on human test subjectsusing one amp of current at 750,000 hertz. The runs were uniformlyconducted, and the data obtained is shown in Table 5, as averageimpedance per square inch.

Further testing of the electrode pad was carried out by weighing the padand heat sealing it into an aluminum foil laminate pouch having amoisture vapor transmission rate not greater than 0.016 g/100 in² /24hrs. when tested at 37° C. with 90% relative humidity on one side anddry air on the other. This procedure was repeated several times, and thesealed pads are placed into a Blue M oven at the same time. At two weekintervals, six of the pouches were removed and allowed to stand at roomtemperature for 18 hours. The pouches were then opened, the padsremoved, the pads reweighed, and then electrical impedance and adhesionto a metal plate were tested. The results of this testing are set forthin Table 8.

Petri dish samples of the irradiated adhesive were prepared and testedto see whether the irradiated adhesive supports bacterial or moldgrowth. Each of four plates was inoculated with Serratia marcescens,Micrococcus lutea, E. coli and Candida albicans. One of these inoculatedplates was incubated for two weeks at 2° C., another at 25° C., a thirdat 37° C. and the fourth at 55° C. A fifth plate was left sealed at roomtemperature as a negative control. A sixth plate was left open for 15minutes to room air in a biology lab and allowed to incubate at 25° C.for one week and 37° C. for an additional week. None of the six platesshowed any colony growth. As a positive control, an agar platecontaining minimum nutrients was inoculated with the same bacterial andyeast and incubated at 37° C. Colony growth is seen on this plate after24 hours.

COMPARATIVE EXAMPLE 6

A commercially available electrosurgical pad is used for comparison withthe electrode pad of Example 45. This pad, which was designated"Comparative Pad" throughout this specification, had a viscous gelimpregnated in a reticulated polyurethane sponge, and had a conventionalpressure-sensitive adhesive along the border for adhering the pad to asurface such as mammalian skin. The electroconductive member of the padwas a nickel alloy, and the viscous gel was comprised of 3%Carbopol®934, 3% sodium sodium chloride, sufficient sodium hydroxide toadjust the pH to 7.0, and water.

The various testing carried out on the electrode pad of Example 45 wasrepeated in the same manner, except that inoculation with bacteria andyeast was not carried out. Additionally, the testing involving use ofthe Blue M oven was conducted so that these samples and the othersamples were placed into the oven at the same time and also removed fromthe oven and otherwise treated at the same time. In Tables 5-8, the dataobtained are set forth.

EXAMPLE 46

A conductive adhesive was prepared using the procedures of Example 45having the following formulation:

    ______________________________________                                        Ingredient             Percent by Weight                                      ______________________________________                                        Polyvinylpyrrolidone (PVP K 90, GAF)                                                                 20                                                     Polyethylene glycol 300 (Carbowax 300                                                                25                                                     Sentry Grade, Union Carbide)                                                  Magnesium Acetate (Reagent Grade,                                                                    5                                                      J.T. Baker)                                                                   Water                  50                                                     Ultramarine Blue (Whitaker, Clark                                                                    0.5                                                    & Daniel                                                                      ______________________________________                                    

Industrial Applicability

The present invention is concerned with a novel water-insoluble,hydrophilic, elastomeric, pressure-sensitive adhesive. This adhesive isuseful either as a coating on a supportive web-like substrate or as aself-supporting layer. When supported by a web-like substrate, thisadhesive is useful as an adhesive on a bandage, a wound or burndressing, a sanitary napkin, a diaper, an ostomy device, a decubitusulcer pad, a vibration or impact absorbing material, a sound absorbingmaterial, and a medium for delivering a pharmacologically active agent(drug). In addition, when used as a self-supporting layer, this adhesiveis useful as a cosmetic face mask and for securing a prosthesis orarticle of apparel to a mammalian body. In one embodiment of theadhesive, the adhesive is electrically conductive and is useful as anelectrode adhesive. Illustrative electrodes include a transcutaneouselectrical nerve stimulation electrode, an electrosurgical returnelectrode, and an EKG monitoring electrode.

                  TABLE 1                                                         ______________________________________                                                                    Standard                                                                      Devia-                                                             Average    tion                                              ______________________________________                                        Rolling Ball Tack                                                             Test (ASTM D3121)                                                             (A) Dry (5 runs)   0.04"             0.005                                    (B) Wet (5 runs)   0.03"             0.002                                    Peel Strength                                                                 180° Peel (ASTM 903)                                                   (A) Dry (2 runs)   2.57   lb/in width                                                                             0.69                                      (B) Wet (3 runs)   0.43   lb/in width                                                                             0.09                                      Peel Strength                                                                 90° Peel (ASTM D1876)                                                  (A) Dry (4 runs)   4.34   lb/in width                                                                             1.82                                      (B) Wet (3 runs)   0.98   lb/in width                                                                             0.19                                      Lap Shear                                                                     (A) Dry (2 runs)   1.98   psi       0.46                                      (B) Wet (2 runs)   0.054  psi       0.05                                      Oxygen Permeance (standard cubic                                              feet O.sub.2 /hour/inch.sup.2 at 1 psi pressure                               drop)                                                                         (A) Dry            5.1              --                                        (B) Wet            --               --                                        ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Water Vapor Transmission (ASTM 3833).sup.1                                               Wet             Dry                                                           A1    A2        B1      B2                                         ______________________________________                                        Initial      22.36   13.80     23.97 20.39                                    Weight                                                                        CaCl.sub.2 (g)                                                                Initial      12.04   14.70     7.73  6.40                                     Weight                                                                        Sample (g)                                                                    H.sub.2 O Absorbed                                                                         12.32   11.02     14.30 15.40                                    CaCl.sub.2 (g)                                                                H.sub.2 O Absorbed                                                                         11.89   4.63      28.98 29.84                                    as a percent                                                                  of initial                                                                    sample                                                                        weight                                                                        Actual       1.43    0.68      2.24  1.91                                     Weight Gain                                                                   Sample (g)                                                                    Water Vapor  353.94  316.67    410.92                                                                              442.43                                   Transmission                                                                  Rate                                                                          g/100 in.sup.2                                                                Thickness.sup.2                                                                            0.12    0.10      0.07  0.06                                     (inches)     0.03    0.04      0.01  0.01                                     Std. Dev.                                                                     ______________________________________                                         .sup.1 The conditions maintained in the sealed chamber were 90-95%            humidity and 100° F. ± 1°. The samples were conditioned      for 24 hours. Since the dessicant, CaCl.sub.2, reached 100% absorbency in     24 hours, the test was concluded.                                             .sup.2 Each value represents an average of 5 readings across each sample.

                                      TABLE 3.sup.1                               __________________________________________________________________________                                   Theoretical Formula                            Example                                                                            Polymer (%)                                                                              Plasticizer (%)                                                                        Dose (MR)                                                                           of Dry Adhesive                                __________________________________________________________________________     2   PVA (18%)  PEG 300 (10%)                                                                          2                                                                    Water (72%)                                                    3   PVP (22.5%)                                                                              PEG 300 (10%)                                                                          1.5                                                                  Water (67.5%)                                                  4   PVP (20%)  PEG 300 (20%)                                                                          2                                                                    Water (60%)                                                    5   PVP (17.5%)                                                                              PEG 300 (30%)                                                                          2                                                                    Water (52.5%)                                                  6   PVP (15%)  PEG 300 (40%)                                                                          2                                                                    Water (45%)                                                    7   PVP (12.5%)                                                                              PEG 300 (50%)                                                                          2                                                                    Water (37.5%)                                                  8   PVP (18%)  PEG 300 (10%)                                                                          2                                                                    Water (72%)                                                    9   PVP (16%)  PEG 300 (20%)                                                                          2                                                                    Water (64%)                                                   10   PVP (14%)  PEG 300 (30%)                                                                          2     32% PVP                                                        Water (56%)    68% PEG 300                                    11   PVP (20%)  PEG 300 (10%)                                                                          3.5   67% PVP                                                        Water (70%)    33% PEG 300                                    12   PVP (20%)  PEG 300 (15%)                                                                          3.5   57% PVP                                                        Water (65%)    43% PEG 300                                    13   PVP (20%)  PEG 300 (20%)                                                                          3.5   50% PVP                                                        Water (60%)    50% PEG 300                                    14   PVP (20%)  PEG 300 (25%)                                                                          3.5   45% PVP                                                        Water (55%)    55% PEG 300                                    15   PVP (20%)  PEG 300 (30%)                                                                          3.5   40% PVP                                                        Water (50%)    60% PEG 300                                    16   PVP (20%)  PEG 300 (35%)                                                                          3.5   36% PVP                                                        Water (45%)    64% PEG 300                                    17   PVP (20%)  PEG 300 (40%)                                                                          3.5   33% PVP                                                        Water (40%)    67% PEG 300                                    18   PVP (20%)  PEG 300 (50%)                                                                          3.5   29% PVP                                                        Water (30%)    71% PEG 300                                    19   PVP (20%)  PEG 300 (60%)                                                                          3.5   25% PVP                                                        Water (20%)    75% PEG 300                                    20   PVP (20%)  PEG 300 (70%)                                                                          3.5   22% PVP                                                        Water (10%)    78% PEG 300                                    21.sup.2                                                                           PVP (20%)  PEG 300 (30%)                                                                          3.5   35% PVP                                                        Water (43%)    53% PEG 300                                    22.sup.3                                                                           PVP (20%)  PEG 300 (10%)                                                                          2                                                                    Water (65%)                                                   23   PVP (7.5%) PEG 300 (30%)                                                                          3.5   15% PVP                                             20% Gafquat ®         25% Gafquat ®                                   755 N in H.sub.2 O (62.5%)                                                                              60% PEG 300                                    24   PVP (15.8%)                                                                              PEG 600 (30%)                                                                          2.5   31.4% PVP                                           20% Gafquat ®                                                                        Water (33.3%)  8.6% Gafquat ®                                  755 N in H.sub.2 O (20.8%)                                                                              60% PEG 600                                    25   PVP (11.6%)                                                                              PEG 600 (30%)                                                                          4     23.2% PVP                                           20% Gafquat ®                                                                        Water (16.7%)  16.8% Gafquat ®                                 755 N in H.sub.2 O (41.7%)                                                                              60% PEG 600                                    26   PVP (2.5%) PEG 600 (10%)                                                                          2.5   8.3% PVP                                            20% Gafquat ®         58.3% Gafquat ®                                 755 N in H.sub.2 O (87.5%)                                                                              33.3% PEG 600                                  27   PVP (5.0%) PEG 600 (20%)                                                                          3     12.5% PVP                                           20% Gafquat ®         37.5% Gafquat ®                                 755 N in H.sub.2 O (75%)  50% PEG 600                                    28   PVP (15.8%)                                                                              PEG 300 (30%)                                                                          3     31.4% PVP                                           20% Gafquat ®                                                                        Water (33.3%)  8.6% Gafquat ®                                  755 N in H.sub.2 O (20.8%)                                                                              60% PEG 300                                    29   PVP (11.6%)                                                                              PEG 300 (30%)                                                                          2.5   23.2% PVP                                           20% Gafquat ®                                                                        Water (16.7%)  16.8% Gafquat ®                                 755 N in H.sub.2 O (41.7%)                                                                              60% PEG 300                                    30   PVP (5%)   PEG 300 (20%)                                                                          3.5   12.5% PVP                                           20% Gafquat ®         37.5% Gafquat ®                                 755 N in H.sub.2 O (75%)  50% PEG 300                                    31   20% Gafquat ®                                                                        PEG 300 (10%)                                                                          3.5   64% Gafquat ®                                   755 N in H.sub.2 O (90%)  36% PEG 300                                    32.sup.4                                                                           PAA (20%)  PEG 300 (20%)                                                                          3                                                                    Water (52%)                                                   33.sup.5                                                                           PAA (17.5%)                                                                              PEG 300 (30%)                                                                          3.5                                                                  Water (45.5%)                                                 34.sup.6                                                                           PAA (20%)  PEG 600 (10%)                                                                          2.5                                                                  Water (62%)                                                   35.sup.7                                                                           PAA (20%)  PEG 600 (20%)                                                                          2.5                                                                  Water (52%)                                                   36.sup.8                                                                           PAA (17.5%)                                                                              PEG 600 (30%)                                                                          3                                                                    Water (45.5%)                                                 37   PAA (15%)  PEG 300 (42.5%)                                                                        3     26% PAA                                                        Water (42.5%)  74% PEG 300                                    38   PAA (15%)  PEG 300 (34%)                                                                          1.5   31% PAA                                                        Water (51%)    69% PEG 300                                    39   PAA (15%)  PEG 300 (25.5%)                                                                        1.5   40% PAA                                                        Water (59.5%)  60% PEG 300                                    40   PAA (14%)  PEG 300 (20%)                                                                          2.5                                                       Polyethylene                                                                             Water (65%)                                                        oxide.sup.9 (1%)                                                         41   PAA (18.8%)                                                                              PEG 600 (20%)                                                                          2     49% PAA                                                        Water (61.2%)  51% PEG 600                                    42   PVP (20%)  Sorbitol (30%)                                                                         3.5                                                                  Water (50%)                                                   43   PVP (20%)  Sorbitol (15%)                                                                         3.5                                                                  Water (65%)                                                   44   MVE/MA (20%)                                                                             PEG 600 (20%)                                                                          3.5   50% MVE/MA                                                     Water (60%)    50% PEG 600                                    __________________________________________________________________________     TABLE 3  Footnotes                                                            .sup.1 PVA is polyvinyl alcohol.                                              PAA is polyacrylic acid having a molecular weight of approximately 450,00     and sold by B. F. Goodrich as Carbopol ® 907.                             MVE/MA is GAF's brand of copolymer of methyl vinyl ether and maleic           anhydride.                                                                    The PVP is PVP K90.                                                           .sup.2 The "wet" formula additionally contained 7% ammonium acetate. This     was a conductive adhesive.                                                    .sup.3 This formula additionally contained 5% magnesium sulfate. This was     a conductive adhesive.                                                        .sup.4 This formula additionally contained 8% of 30% ammonium hydroxide       solution.                                                                     .sup.5 This formula additionally contained 7% of 30% ammonium hydroxide       solution.                                                                     .sup.6 This formula additionally contained 8% of 30% ammonium hydroxide       solution.                                                                     .sup.7 This formula additionally contained 8% of 30% ammonium hydroxide       solution.                                                                     .sup.8 This formula additionally contained 7% of 30% ammonium hydroxide       solution.                                                                     .sup.9 This is a 4 million molecular weight polymer sold by Union Carbide     under the trademark Polyox WSRCoag.                                      

                                      TABLE 4*                                    __________________________________________________________________________    Comparative                 Theoretical Formula                               Example                                                                              Polymer (%)                                                                          Plasticizer (%)                                                                       Dose (MR)                                                                           of Dry Adhesive                                   __________________________________________________________________________    1      PVP (20%)                                                                            Water (80%)                                                                           3.5   100% PVP                                          2      PVP (19.8%)                                                                          PEG 300 (1.0%)                                                                        1.5   95% PVP                                                         Water (79.2%) 5% PEG 300                                        3      PVP (19.6%)                                                                          PEG 300 (2.2%)                                                                        1.5   90% PVP                                                         Water (78.2%) 10% PEG 300                                       4      PVP (19.3%)                                                                          PEG 300 (3.4%)                                                                        1.5   85% PVP                                                         Water (77.3%) 15% PEG 300                                       5      PVP (19.0%)                                                                          PEG 300 (4.8%)                                                                        1.5   80% PVP                                                         Water (76.2%) 20% PEG 300                                       __________________________________________________________________________     *The PVP is PVP K90.                                                     

                  TABLE 5                                                         ______________________________________                                        (Impedance Test)                                                                                          Ratio of Std.                                                                 Deviation per sq.                                                             in. to Avg.                                               Average Im-                                                                            Standard   Impedance per                                             pedance per                                                                            Deviation  sq. in.                                                   square inch.sup.1                                                                      Per sq. in.                                                                              (Measure of Pro-                                          (ohms/sq. in.)                                                                         (ohms/sq. in.)                                                                           duct Uniformity)                                  ______________________________________                                        Using Stainless                                                               Steel Plate                                                                   (A) Example                                                                             0.070      0.020      --                                            45 Pad.sup.2                                                                  (B) Comparative                                                                         0.078      0.018      --                                            Pad.sup.3                                                                     Using Human                                                                   Subjects                                                                      I. Male                                                                       A. Example                                                                              0.586      0.163      0.279                                         45 Pad.sup.2                                                                  B. Comparison                                                                           0.387      0.108      0.323                                         Pad.sup.3                                                                     II. Female                                                                    A. Example                                                                              0.878      0.267      0.304                                         45 Pad.sup.2                                                                  B. Comparison                                                                           0.574      0.185      0.322                                         Pad.sup.3                                                                     ______________________________________                                         .sup.1 Each value represents 15 runs.                                         .sup.2 This pad had an active electrode area of 20 square inches.             .sup.3 This pad had an active electrode area of 24 square inches.        

                  TABLE 6                                                         ______________________________________                                        (Peel Strength - 180°).sup.1                                                                     Ratio of Standard                                            Average                                                                              Standard  Deviation to Average                                         Adhesion                                                                             Deviation Adhesion                                                     (lbs/in.                                                                             (lbs/in.  (Measure of Pro-                                             width) width)    duct Uniformity)                                    ______________________________________                                        I. Using Steel                                                                Plate                                                                         A. Example 0.362.sup.2                                                                            0.043      0.121                                          45 Pad                                                                        B. Comparative                                                                           0.945.sup.2                                                                            0.196      0.207                                          Pad                                                                           II. Using Thigh                                                               of Female                                                                     Human                                                                         Subjects                                                                      A. Example 0.42.sup.3                                                                             0.043     0.24                                            45 Pad                                                                        B. Comparative                                                                           0.79.sup.3                                                                             0.31      0.39                                            Pad                                                                           III. Using Thigh                                                              of Male Hu-                                                                   man Subjects                                                                  A. Example 0.43.sup.3                                                                             0.09      0.21                                            45 Pad                                                                        B. Comparative                                                                           --       --        --                                              Pad.sup.4                                                                     ______________________________________                                         .sup.1 In carrying out these tests, it was noted that the pull force          remains relatively more constant with the Example 45 pad than the             comparative pad.                                                              .sup.2 This value represents 30 runs.                                         .sup.3 This value represents 15 runs.                                         .sup.4 Data were not taken since the male subjects, with their unshaven       legs, experience painful pulling upon pad removal.                       

                  TABLE 7                                                         ______________________________________                                        % of Human Subjects Experiencing                                              Irritation Upon Pad Removal*                                                  ______________________________________                                        I. Male                                                                       (A) Example 45 Pad  0                                                         (B) Comparative Pad                                                                              47                                                         II. Female                                                                    (A) Example 45 Pad .06                                                        (B) Comparative Pad                                                                              66                                                         ______________________________________                                         *Fifteen tests were carried out for each pad type.                       

                  TABLE 8.sup.1                                                   ______________________________________                                                    week week    week   week week week                                            2    4       6      2    4    6                                   ______________________________________                                                       Average      Standard                                          Impedance Test Using                                                                         Impedance    Deviation                                         Stainless Steel Plate.sup.2                                                                  (ohms)       (ohms)                                            (A)  Heat-Aged Example                                                                           1.261  1.208                                                                              1.372                                                                              0.306                                                                              0.373                                                                              0.226                                45 Pad                                                                   (B)  Heat-Aged Com-                                                                              0.710  0.810                                                                              1.116                                                                              0.129                                                                              0.080                                                                              0.166                                parative Pad                                                             Peel Strength - 180° Standard                                          Using Stainless                                                                              Average Adhesion                                                                           Deviation                                         Steel Plate.sup.4                                                                            (g/in. width).sup.3                                                                        (g/in. width)                                     (A)  Heat-Aged Example                                                                           142.7  139.2                                                                              142.1                                                                               10.8                                                                              37.1 38.4                                 45 Pad                                                                   (B)  Heat-Aged Com-                                                                              555.4  435.8                                                                              487.5                                                                              211.8                                                                              69.7 37.9                                 parative Pad                                                                          Average Weight                                                                           Standard                                                           Loss (%).sup.5                                                                           Deviation                                             (A)  Heat-Aged Example                                                                           -0.5   N/A  -0.8 0.2% N/A  0.7%                                 45 Pad                                                                   (B)  Heat-Aged Com-                                                                              -0.8   N/A  -3.9 0.5% N/A  2.8%                                 parative Pad                                                             ______________________________________                                         .sup.1 The samples were aged at 55° C. in a Blue M oven, Model         E200431.                                                                      .sup.2 The impedance test on these aged samples was run identically to th     Table 5 impedance test using a stainless steel plate.                         .sup.3 Each value represents 6 runs.                                          .sup.4 The peel strength test on these aged samples was run identically t     the Table 6 peel strength test using a stainless steel plate.                 .sup.5 Each value represents 36 runs.                                    

I claim:
 1. An electroconductive, water-insoluble, hydrophilic,elastomeric pressure-sensitive adhesive comprising a gel ofpolyvinylpyrrolidone cross-linked by ionizing radiation, a polyalkyleneglycol plasticizer, water and a salt selected from ammonium acetate,magnesium acetate or magnesium sulfate,wherein said cross-linked gel isformed by irradiation of a solution or dispersion of said salt and saidpolyvinylpyrrolidone in said water and said plasticizer; and whereinsaid cross-linked gel retains said plasticizer within a cross-linkedthree-dimensional matrix of said polyvinyl pyrrolidone.
 2. The adhesiveof claim 1 wherein said plasticizer is present in an amount ranging fromabout 0.5 to 4 times the weight of said polymer.
 3. The adhesive ofclaim 1 wherein said salt is magnesium acetate.
 4. The adhesive of claim1 wherein said plasticizer is polyethylene glycol.
 5. The adhesive ofclaim 4 wherein said glycol has a molecular weight of about 300 or 600.6. The adhesive of claim 5 wherein said glycol is present in an amountthat is from about 0.75 to 1.5 times the weight of said pyrrolidone. 7.The adhesive of claim 1 wherein the said solution or dispersioncomprises(a) about 18 to 22 percent by weight of polyvinyl pyrrolidone,(b) about 25 percent by weight of polyethylene glycol having a molecularweight of about 300, (c) about 5 to 7 percent by weight of magnesiumacetate, and (d) water.
 8. An electrode comprising an electricallyconductive member and the electroconductive adhesive of claim 1, saidadhesive being adapted to attach said member to mammalian skin.
 9. Theelectrode of claim 8 which comprises an electrosurgical returnelectrode, a transcutaneous electrical nerve stimulation electrode or anEKG monitoring electrode.
 10. The electrode of claim 8 which comprisesan electrosurgical return electrode.
 11. The electrode of claim 8wherein said electroconductive adhesive is coated on a web-likesubstrate.
 12. An electrosurgical return electrode comprising anelectrically conductive member in electroconducting association with anelectroconductive pressure-sensitive adhesive coated on a web-likesubstrate and adapted to attach said member to mammalian skin,saidadhesive being a radiation cross-linked gel comprising about 20 percentby weight of K-90 polyvinyl pyrrolidone, about 25 percent by weight ofpolyethylene glycol having a molecular weight of about 300, about 5percent by weight of magnesium acetate, and about 50 percent by weightof water.
 13. The electrode of claim 12 wherein said adhesive contains acompatible preservative.